Beam scanning method and apparatus



C. S. NUNAN BEAM SCANNING METHOD AND APPARATUS July 6, 1965 4Sheets-Sheet; 1

Original Filed March 9, 1959 Attorney July 6, 1965 c. s. NUNAN BEAMSCANNING METHOD AND APPARATUS 4 Sheets-Sheet 2 Original Filed March 9,1959 INVENTOR. Craig S. Nunan July 6, 1965 c. s. NUNAN 3,193,717

BEAM SCANNING METHOD AND APPARATUS Original Filed March 9, 1959 4Sheets-Sheet 3 INVENTOR. Craig S. Nunan Attorney y 6, 1965 c. s. NUNAN3,193,717

BEAM SCANNING METHOD AND APPARATUS Original Filed March 9, 1959 4Sheets-Sheet 4 INVENTOR. Craig S. Nunan Arrorhey United States Patent3,293,717 BEAM SCANNING METHOD AND APPARATUS Craig S. Nunan, Los AltosHills, Calif, assignor to Varian Associates, Palo Alto, Calif, acorporation of California Continuation of application Ser. No. 798,064,Mar. 9, 1959. This application July 3, 1961, Ser. No. 123,942 21 Claims.(Cl. 313-76) This invention relates in general to beam scanners andscanning methods and more particularly to a novel beam scanner assemblyfor use with particle accelerators for research, therapy, sterilization,polymerization and the like and with other apparatus Where there is aneed for bending particle beams and causing the bent beams to scan asurface.

This application is a continuation of application Serial No. 798,064;filed March 9, 1959, now abandoned.

It is desirable to mount particle accelerator sections on a horizontalaxis to minimize shielding and maintenance and to facilitate futureaddition of accelerator sections, while on the other hand it is alsonormally desirable to scan objects from above.

There has been a need for an economical particle beam scanner assemblywhich incorporates the above features, and such a beam scanner assemblyshould include means for bending a high energy particle beam and causingthe bent beam to scan across a particular surface. Normally a beam ofhigh energy particles includes particles of many different energies, andpreviously difliculty has been encountered in bending a beam ofdifferent energy particles and then deflecting all of the particles ofthe bent beam through the same angle to scan a surface. Furthermore,beam focusing difficulties have been encountered in attempting to bendsuch a beam of high energy particles.

The principal object of the present invention is to provide a novel beamscanning method and efflcient beam scanner assembly wherein a beam ofparticles such as electrons, protons, etc., is bent; then all theparticles of the bent beam are deflected through approximately the sameangle to scan a surface.

One feature of the present invention is the provision of a novel beamscanner assembly rotatable about the axis of a particle beam to causethe beam to scan a surface positioned at any desired angle with relationto the axis of the beam.

Another feature of the present invention is the provision of a novelbeam scanner assembly including a bending magnet and a scanning magnetto cause a particle beam containing particles of different energies toscan evenly across a surface positioned at an angle with relation to theaxis of the particle beam.

Another feature of the present invention is the provision of a novelbending magnet with its pole pieces aligned along opposite sides of aparticle beam and its input and output edges inclined with relation tothe trajectory of the particle beam to change the trajectory ofparticles of different energies through the same angle.

Another feature of the present invention is the provision of a novelbending magnet, an edge of which is contained in a rotatable section ofthe magnet for changing the angle of inclination between a particle beamand the magnet.

Another feature of the present invention is the provision of a novelscanning magnet whose pole faces have a magnetic field gradienttherebetween to deflect all the particles of a particle beam with aparticle energy gradient thereacross through approximately the sameangle.

Another feature of the present invention is the provision of a novelbending magnet which deflects particles of different energies throughthe same angle and mechanical means for imparting an oscillatory motionto the bending magnet about the axis of the particle beam directed intothe bending magnet to cause the deflected particles to scan evenlyacross a surface at an angle to the particle beam axis.

Still another feature of the present invention is the provision of aquadrupole magnet for focusing a particle beam before the beam is bentand caused to scan a surface thereby to adjust the size of theirradiating spot of particles.

Still another feature of the present invention is the provision of anovel method of scanning a particle beam containing particles ofdifferent energies wherein the particle beam is transformed into aparticle beam directed in a different direction and then transformedinto a scanning beam in which a ray containing all the particles of oneenergy level is scanned through substantially the same angle as the raycontaining all the particles of a different energy level.

Still another feature of the present invention is the provision of thenovel method for scanning a particle beam of the last aforementionedfeature wherein when the particle beam is transformed into a. particlebeam directed in a different direction the particles of differentenergies are traveling in substantially the same direction.

Still another feature of the present invention is the provision of anovel method for scanning a particle beam with a particle energygradient thereacross including the step of transforming each raycontaining all the particles of one energy level into a scanning raywhich scans through substantially the same angle as a ray containing allthe particles of a different energy level.

These and other features and advantages of the present invention will bemore apparent after a perusal of the following specification taken inconnection with the accompanying drawings wherein,

FIG. 1 is a perspective view of an electron linear acceleratorembodiment of the present invention showing the beam scanner assemblypartially broken away and the trajectories of electrons of somewhat.different energies through the novel beam scanner assembly,

FIG. 2 is an enlarged cross-section view of the electron orientation inan electron beam within the accelerator section of FIG. 1 taken alongline 2-2 in the direction of the arrows,

FIG. 3 is an enlarged cross-section view of the structure of FIG. 1 andthe electron orientation in an electron beam passing therethrough takenalong line 33 in the direction of the arrows,

FIG. 4 is a cross-section view of the structure of FIG. 3 and theelectron orientation in an electron beam passing therethrough takenalong line 44 in the direction of the arrows,

FIG. 5 is a perspective view of the lower portion of the novel bendingmagnet showing the fringe magnetic fleld forces on a particle emergingtherefrom for two possible positions of the output surface of themagnet,

FIG. 6 is a cross-section view of the structure of FIG. 3 and theelectron orientation in the electron beam upon passing therethroughtaken along line 66 in the direction of the arrows,

FIG. 6A is a modification of the magnet structure shown in FIG. 6,

FIG. 7 is a cross-section view of a further embodiment of the presentinvention, and

FIG. 8 is a cross-section view of one orientation of the structure ofFIG. 7 taken along line 88 in the applicable for bending and scanningbeams of other particles such as, for example, protons. Also the novelbeam scanner is adaptable for use with both pulsed and con tinuousbeams.

Referring now to the drawings, the operation of the beam scanner willfirst be described in general followed by a more complete description ofits novel components.

A beam of electrons 11 emerging from an accelerating section 12 of alinear accelerator positioned, for example, horizontally is passed intoan evacuated chamber 13 comprising a horizontal tube 14 with arectangular tube branch 15 projecting downwardly therefrom, and a flaredscanner section 16 projecting downwardly from the end of the branch 15and with an elongated vacuum tight window 17 at the end thereof (seeFIG. 3), the scanner section 16 being rectangular in a horizontalcross-section with the longer side of the rectangle alignedperpendicularly to the axis of the tube 14. The tube 1 is axiallyaligned with the accelerator section 12 and is coupled thereto by arotatable coupling 18 permitting rotation of chamber 13 about the axisof electron beam 11. The opposite end of tube 14 contains a circularvacuum tight window 19, and the side of branch 15 toward the coupled endof tube 14 contains a gradual bend at its junction with tube 14permitting the electron beam 11 passing through tube 14 to be bentdownwardly and directed through branch 15 as described below. To preventirradiation damage, the portions of chamber 13 which are subject toelectron bombardment from stray electrons are lined with liquid cooledaluminum.

A quadrupole focusing magnet 21 encircles and is axially aligned withtube 14 at its end adjacent accelerator section 12 for creating afocusing magnetic field within tube 14. A power supply (not shown) witha current control adjustment supplies direct current to focusing magnet21 for focusing electron beam 11 either horizontally or vertically tothereby change the size of the irradieting beam of electrons issuingfrom the beam scanner as described below.

A bending magnet 22 is positioned with its pole pieces verticallyaligned along opposite sides of electron beam 11 outside chamber 13 atthe position where branch 15 leaves tube 14 for bending electron beam 11through an angle of 90. The bending magnet 22 is a DC. electromagnetmade up of two pole pieces mounted on a yoke 23, a north pole 24 with aset of windings 25 and a south pole 26 with a set of windings 27. Thebending magnet 22 is energized by applying current to the windings 25and 27 from a DC. power supply (not shown) with a current controladjustment. An upper input surface 28 of bending magnet 22 is inclinedat an angle of approximately 30 from vertical, and a lower outputsurface 29 is declined approximately 45 from horizontal.

When the bending magnet 22 is not operating, electron beam 11 will passstraight through tube 14 and out circular window 19; when the bendingmagnet 22 is operating, the electron beam '11 is bent downwardly throughan angle of 90 due to the effect of the magnetic field between the poles24 and 26 and passes through branch 15. An electron beam with an averageelectron energy of, for example, 12 mev. will be bent through 90 by thebending magnet 22 as described above with a fiield of approximately 3500gauss. Electrons with energies greater than the average energy of theelectron beam 11 will traverse a longer trajectory between the magneticpoles 24 and 26 than electrons of lesser energy before being deflectedthrough an angle of 90. For this reason the lower output surface 29 ofbending magnet 22 is tilted at a declination of approximately 45 so thatelectrons of greater energies will traverse proportionately greatertrajectory lengths between the poles 24 and 26, and all electrons on theoriginal beam axis will emerge from bending magnet 22 parallel to oneanother after having been deflected through an angle of 90".

A rotatable, solid, semicircular section 32 of magnet material is fittedin the input portion of each of poles 24 and 26 between the windings andthe pole faces of bending magnet 22 and each of these rotatable sections32 has a flat exposed surface, these flat surfaces making up inputsurface 28 (see FIG. 3). These semicircular sections can be rotated, forexample, by means of a handle 33 which can be connected to both of therotatable sections 32 to rotate these sections simultaneously, or thehandle can rotate just one section at a time as shown. The input surface23 of bending magnet 22 can be inclinedat any angle to the vertical byadjustment of these rotatable sections 32 to thereby change the size ofthe irradiating beam of electrons issuing from the beam scanner assemblyas further described below. Interchangeable sections, each with a flatinput surface inclined at a different angle, can be used in place ofrotatable sections 32 for selecting a particular angle of inclinationfor input surface 28.

The magnetic field strength of bending magnet 22 is adjusted so that anelectron with an average energy of the electrons in the beam 11 followsa trajectory 34 between the poles of the bending magnet 22 and emergesfrom bending magnet 22 within chamber 13 approximately half-way alongthe declined output surface 25 When the preceding is true, an electronwith, for example, 20% less energy than an average energy electron ofthe beam 11 follows a shorter trajectory 35 than the trajectory 34 ofthe average energy electron and emerges from the output surface 25 afterbeing deflected through an angle of Similarly, an electron with, forexample, 20% greater energy than the average energy electron of the beam11 follows a longer trajectory 36 between the poles of bending magnet 22but emerges from bending magnet 22 traveling parallel to electrons oflower energies.

The output surface 29 of bending magnet 22 can be set at angles greateror less than 45 from the direction of beam 11 by, for example, providingrotatable semicircular sections to change the angle of inclination ofoutput surface 29 or tilting the entire bending magnet if an angle otherthan 45 be required to make electrons 'of all energies emerge parallelto one another.

Due to the manner in which bending magnet 22 deflects electrons ofdifferent energies through the same angle, a bent electron beam 37emerges from the output surface 29 of bending magnet 22 containing anelectron energy gradient thereacross. The above described relationshipsbetween the beam and the bending magnet apparatus result in anapplication of particle deflecting forces along the trajectories of thedifferent energy particles passing through the bending magnet apparatussuch that for all the different particle trajectories through theapparatus, the deflecting forces applied to any given particle aresubstantially proportionate to the energy of that particle. Therefore,particles of all energies passing through the apparatus will bedeflected through substantially the same angle as pointed out in greaterdetail hereinafter. The bent electron beam 37 is then directed betweenthe pole pieces of a scanning magnet 38, an AC; electromagnet thatdeflects the bent electron beam 37 back and forth in a directionperpendicular to the axis of electron beam 11 to cause the bent electronbeam 37 to scan across a package located below the scanner section 16 asfurther described below. The scanning magnet 38'comprises a pole piece39 with a concave pole face 41 and a set of windings 42 and a pole piece43 with a convex pole face 44 and a set of windings 45. The pole pieces39 and 43 are positioned horizontally on the outside of chamber 13 nearthe top of the flared scanner section 16 by means of a yoke 46 and arealigned with the axis of electron beam 11 with the convex pole face 44of pole piece 43 on the side of scanner section 16 adjacent the highenergy side of the bent electron beam 37. The pole faces 41 and 44 ofscanning magnet 38 are, for example, hyperbolic vertical planes fordeflecting all the electrons of a particle beam with a particle energygradient thereacross through substantially the same angle in the mannerdescribed below. A current is passed through the windings 42 and 45 froma power supply (not shown) creating a magnetic field within chamber 13between pole faces 41 and 44. A programmer (not shown) which comprises,for example, a group of beam switch- 5 rection of the magnetic fieldbetween pole faces 41 and 44 as a function of time. As the polarity ofthe pole pieces of the scanning magnet 38 is reversed, the bent beam isdeflected back and forth within scanner section 16.

Since the pole faces 41 and 44 of scanning magnet 38 are curvedsurfaces, the high energy side of the bent electron beam 37 adjacent theconvex pole face 44 will be acted upon by a greater component of thescanning magnet magnetic field than the lower energy side at any oneinstant as described in detail below, and thus by proper selection ofthe strength and shape of the scanning magnet, electrons of differentenergies are deflected back and forth through approximately the sameangle. The amount which the bent electron beam 37 is deflected from itsnormal path by scanning magnet 38 will depend upon the strength of themagnetic field of scanning magnet 38.

The bent electron beam 37 is deflected back and forth within the flaredscanner section 16 of chamber 13 and passes out through elongated window17 to scan an area 47 of a package 4-8 which is moved beneath thescanning beam by means of a conveyor (not shown) so that the surface ofthe package 48 is irradiated by the electron beam in a desired pattern.By applying a voltage of a modified triangular waveform to scanningmagnet 38, the beam will scan across the package 48 at a constant rateto produce a zig-zag pattern on the moving package, or a pattern ofparallel paths across the package 48 can be produced by applying amodified sawtooth waveform to scanning magnet 38.

The beam scanner assembly including the tube 14 and branch 15 of chamber13, focusing magnet 21, deflecting magnet 22 and scanning magnet 38 ismounted in a housing 49, and this housing 49, like the chamber 13, iscoupled by rotatable coupling 18 to the accelerator section 12 ,forrotation about the axis of electron beam 11 to direct the scanning beamin any direction about the axis of the electron beam 11. The beam 11 canbe bent through angles other than 90, and in such case, chamber 13 wouldbe of such shape as to allow the bent beam to pass therethrough.

As a further embodiment of the novel beam scanner assembly, the housing49 itself is an evacuated chamber with a flared section on the bottomthereof and with the focusing, bending and scanning magnets containedtherein eliminating the need for the chamber 13. In such an embodimentthe bending and scanning magnets are provided with positioning means toposition the magnets so that electron beam 11 can be bent through anydesired angle. Also, bending magnet 22 can be adjusted so that electronsof different energies converge at output window 17 in order to minimizewindow width or diverge toward the output window in order to achieve abroader scanning pattern.

Referring now to FIG. 2 there is shown an enlarged cross-section view ofthe electron orientation in the electron beam 11 of FIG. 1. Since allthe electrons of the same energy are not concentrated at any one pointon the cross section of the electron beam, the beam scanner assemblymust focus all the electrons of the same energy level so that theelectron beam scans properly. For purposes of illustration, electronstraveling at different positions on the cross section of the electronbeam will be examined to show the effect on them while passing throughthe novel beam scanner. To study the effect of the beam scanner, points51, 52, 53, 54 and 55 are respectively selected on the axis, at thebottom, at the top, at the left side and at the right side of theelectronbeam 11 for examination.

Referring noW to FIG. 3 there are shown the electron trajectories forthe electron beam 1 1 and the structure of the novel beam scanner on aplane taken vertically through the electron beam 11 and the scanningmagnet 38 and between the pole pieces of the bending magnet 22. In thisfigure are shown the vertical positions 51, 52 and 53 taken from thecross section of the electron beam in FIG. 2 and the trajectories 34, 35and 36 through the bending magnet 22 for electrons of the differentenergy levels. For trajectory 34 electrons of average energy travelingalong the axis 51 of the electron beam 11 will traverse a path 56through bending magnet 22 and will emerge from output surface 39 afterhaving been deflected through an angle of Average energy electronstraveling along the bottom 52 and the top 53 of the electron beam 11will traverse paths 57 and 58, respectively, the path 57 being shorterand the path 58 being ionger than the path 56. In a similar mannerelectrons of energy 20% below average traveling along the verticalpositions 51, 52 and 53 of the electron beam 11 will traverse paths 59,61 and 62, respectively through the bending magnet 22 and electrons withenergy 20% above average traveling along vertical positions 51, 52 and53 of the electron beam 1-1 will traverse paths 63, 64 and 65,respectively through bending magnet 22, the electrons that weretraveling along the bottom position 52 of the electron beam 11 alwaysbeing deflected through an angle slightly less than 90 and those thatwere traveling along the top posit-ion 53 always being deflected throughan angle of slightly greater than 90. All the electrons of thesameenergy level will pass through a focal point after emerging from thelower face 29 of bending magnet 22, the focal points for the average,20% below average and 20%. above average energy trajectories being 66',67 and 68, respectively, and after passing through the focal points forthe respective electron energy levels the electrons of the same energylevel which were traveling at the top of the electron beam 11 and thoseat the bottom will follow diverging paths.

Referring now to FIG. 4 there is shown a cross section of the structureof FIG. 3 taken along line 4-4 in the direction of the arrows andshowing the paths through the beam scanning assembly of the electronshorizontally displaced from the axis of the electron beam 11. Electronsof all energies traveling along the sides of the electron beam 1-1 atthe left and right positions 54 and 55 respectively behave essentiallythe same as an electron traveling along the axis position 51 with regardto the deflecting effects discussed above in referring to FIG. 3.Electrons traveling along the vertical axis of electron beam 11 passthrough bending magnet 22 along a median plane 69 midway between polepieces 24 and 26. However, electrons such as traveling along the leftand right positions 54 and 55, respectively, horizontally displacedacross the electron beam 11 travel off axis paths 71 and 72,respectively, through bending magnet 22 and awarded upon by the focusingand defocusing effects of the fringe magnetic field bet-ween pole pieces24 and 26 as described in detail below,

Referring now to FIG. 5 there is shown the lower portion of bendingmagnet 22 and the fringe magnetic field forces affecting the bentelectron beam 37 emerging vertically downwardly therefrom with theoutput surface 29 declined at an angle of 45 from the horizontal and, asan alternative for purposes of illustration, with an output surface 73positioned horizontally. When an electron beam emerges from between thepoles of a magnet and normal to the output surface thereof withelectrons traveling outside of the median plane 69 such as along theoff-axis paths 71 and '72, the electron beam is only affected by thebending effects of the magnet and is not deflected toward or away fromthe' pole pieces. A fringe magnetic field denoted by the line of flux 74at the horizontal output surface 73 affects electrons traveling alongmedian plane 69 with a magnetic field force 75 that is perpendicular tothe electron path and to the magnet pole faces thereby producing a beambending force '76 which bends the beam as described above, but thefringe magneticfield affects electrons traveling along the off-axispaths 71 and 72 with a magnetic field force 77 which has a component 78that is perpendicular to the electron path and to the magnet pole facesthereby producing a beam bending force'79 and a component 81 that isparallel to the electron path thereby producing no effect on theelectrons.

However, when an electron beam emerges from between the poles of amagnet and is not normal to the output surface thereof, electronstraveling outside the median plane 6 9 are affected by a force tendingto deflect them toward or away from the median plane depending uponwhether the electrons are respectively being deflected away from ortoward the normal to the output surface from which the electron beamemerges. A fringe magnetic field denoted by a flux line 82 at the outputsurface 29 which is declined at an angle of approximately 45 affectselectrons traveling along median plane 69 with a magnetic field force 33that is perpendicular to the electron path and to the magnetic polefaces thereby producing a beam bending force 84 which bends the beam asdescribed above, but this fringe magnetic field affects electronstraveling along off-axis paths 71 and 72 with a magnetic field force 85which has a component 86 that is perpendicular to the electron path andto the magnet pole faces thereby producing a beam bending force 87 and acomponent 88 that lies in a plane with the off-axis electron path, thisplane containing the component 88 and the ofhaxis electron path beingparallel to the median plane 69. The component 38 itself can be brokeninto .two subcomponents 89 and 91 within the plane of component 8 8 andthe off-axis electron path, subcomponent 89 being perpendicular to theelectron path thereby producing a beam defocusing force 92 andsubcomponent d1 being parellel to the electron path thereby producing noeffect on the electrons. Since the fringe magnetic field is caused byfiux lines which bow out from the output surface of the magnetic field,electrons traveling along off-axis paths 71 and 72 will be affected bybeam defocusing forces in opposite directions so that the whole beam isdefocused.

Thus, if a magnet bends an electron beam toward the normal to an outputface, defocusing occurs in the fringe magnetic field at that face whileif the beam is bent away from the normal to that output face a focusingeffect takes place in the fringe magnetic field. However, at an inputface of a magnet, an electron beam that is bent toward the normal tothat face upon entering the magnet is caused to be focused in the fringemagnetic field while an electron beam that is bent away from the normalis caused to be defocused.

The defocusing effect is created at the output surface 29 of bendingmagnet 22 when output surface 29 is inclined approximately 45 from thehorizontal in order that electrons of different energy levels emergeparallel to one another. The input surface 23 of bending magnet 22 isadjustably inclined, for example, at approximately from vertical bymeans of the rotatable sections 32 to focus the electron beam 1-1 towardthe median plane 69 by means of the focusing effect on electron beam 11by the fringe magnetic field at the bending magnet input surface tocompensate for the above described defocusing effect at the outputsurface, thereby changing the Width of the irradiating spot on package48. For the purposes of the illustration here, the input surface 28 isinclined at only 30 while the output surface 29 is declined at so thatthe beam emerging from bending magnet 22 diverges to create anirradiating spot wider than the width of electron beam 11.

Referring now to FIG. 6 there is shown a cross-section View of the lowerportion of the scanning magnet 33 showing a cross section of bentelectron beam 37 as it is leaving the magnetic field of the scanningmagnet 38. The bent electron beam 37 describes in cross section somewhatof an elliptical spot with the electron trajectories of differentenergies linearly disbursed thereacross. Within the cross section of thebent electron beam 37 are separate elliptical cross sections for theaverage, 20% below average, and 20% above average energy electrontrajectories 34, 35 and 36 with the paths of the electrons originallytraveling at positions 52, 53, 54 and 55 of electron beam 11 lying onthe ends and sides of the ellipse for each energy level. Bent electronbeam 37 is deflected back and forth within scanning magnet 33 through anapproximately rectangular area 93.

Due to the curved surfaces of the pole faces of scanning magnet 3%, theflux density of the magnetic field between the pole pieces of scanningmagnet 33 increases from the concave pole face 4-1 to the convex poleface 4-4. As the radius of curvature of convex pole face 4-4 is madegreater than the radius of curvature of concave pole face 41, the fluxdensity gradient between pole faces 41 and 4% increases, and, thedesired flux density gradient between pole faces 41 and 44 is achievedby use of pole faces with the proper difference between their radii ofcurvature. The scanning magnet magnetic field component perpendicular tothe direction of the scan acts upon the bent electron beam 37 to scan itback and forth, and since the fiux density gradient between pole faces41 and 44 increases toward the convex pole face it, all the electrons ofbent electron beam 37 with its high energy side adjacent convex poleface 44 will be scanned through approximately the same angle. Thus it isseen that the relationship between the beam having an energy gradientthereacross and the scanning ma net magnetic field is such thatdeflecting forces are applied along the trajectories of the differentenergy particles through the magnetic field such that for all thedifferent particle trajectories through the magnetic field thedeflecting forces applied to any given particle are substantiallyproportionate to the energy of that particle. Therefore, particles ofdifferent energies will be simultaneously deflected throughapproximately the same angle.

The pole faces of the scanning magnet 33 can be of any other shape, forexample, vertical planes which are semi-cylindrical or V-shaped inhorizontal cross section, or even planes curved in a vertical direction,as long as there is a flux density gradient therebetween. For purposesof illustration the concave pole face 41 in FIG. 6A is V- shaped inhorizontal cross section and there will still be a flux density gradientbetween the pole pieces increasing from concave pole piece 39' to convexpole piece 43.

Referring now to FIGS. 7 and 8 there is shown a further embodiment ofthe present invention. The electron beam 11 emitted from acceleratingsection 12 is passed into an evacuated housing 94 in which it is bentthrough an angle of, for example, by means of a bending magnet 95similar to bending magnet 22 described above. The electron beam isdeflected back and forth perpendicular to the axis of electron beam 11by mechanical movement of the bending magnet 95 to impart a scanningmotion to the bentbeam. Mechanical movement of bending magnet 95' isaccomplished by, for example, imparting an oscillatory motion to a yoke96 of bending magnet 95 by rotating the yoke 96 in ball bearing sleeves97 about an axis coincident with the axis of the electron beam 11. A rod93 is pivotally connected to the yoke 96 by a pivot 99 and to a flywheel1d]. by a pivot 1132. The flywheel 161 is mounted on a drive shaft 103which is in turn driven by a motor 104 fixed on the inside of the top ofhousing 94, and when the flywheel 101 rotates, the rod 98 is moved upand down imparting an oscillatory motion to bending magnet 95.

As is apparent from the above, the size of the scanning spot can beadjusted in various ways. The width of the spot in the direction of scanmay be adjusted, for example, by changing the angle of the input surface28 of bending magnet 22 or by first focusing the beam with thequadrupole focusing magnet 21 and the length of the spot by changing theangle of the output surface 29 of bending magnet 22, by varying thefield strength of bending magnet 22, or by first focusing the beam withquadrupole focusing magnet 21 (see FIG. 1).

The axis of accelerating section 11, of course, need not be horizontal,but this orientation is usually more advantageous.

Since many changes could be made in the above construction and manyapparently Widely different embodiments of this invention could be madeWithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A bending magnet for bending a particle beam whereby after the beamis bent there is a particle energy gradient across the bent beam saidbending magnet comprising opposing pole pieces adapted to be alignedalong opposite sides of the particle beam, said pole pieces having theiroutput surface tilted at an acute angle to the high energy side of theparticle beam which has emerged from the output surface so thatparticles of greater energies will travel longer trajectories throughsaid bending magnet and thereby particles of all energies will bedeflected through substantially the same angle, said acute angle beingless than 60", said acute angle being measured, between any given highenergy side particle trajectory emanating from said output surface andsaid output surface, in a direction rotated away from the lower energyside of said bent beam having a particle energy gradient thereacross.

2. The bending magnet of claim 1 including means for positioning theinput surface of said magnet at different angles relative to theparticle beam directed into said bending magnet including a rotatablesection of magnetic material fitted in the input portion of each of saidpole pieces, said rotatable sections having a flat exposed surface whichoperates as the input surface of said bending magnet whereby saidrotatable sections can be Iotatably positioned to change the angle ofinclination of the input surface of said bending magnet with relation tothe particle beam directed into said bending magnet.

3. The bending magnet of claim 1 including means for adjustablypositioning the output surface of said pole pieces at a selected acuteangle with the high energy side of the particle beam which has emergedtherefrom for deflecting particles of different energies throughselected angles.

4. Means for imparting a scanning motion to a particle beam with aparticle energy gradient thereacross comprising an electromagnet havingwindings thereon, said electromagnet having a pair of pole piecesadapted and arranged to provide a flux density gradient therebetweensaid particle beam being adapted and arranged in relation to saidelectromagnet such that said particle beam is directed between the polefaces of said electromagnet with the particles of greater energyarranged to pass through a portion of the magnetic field with acorrespondingly greater flux density and the particles of lesser energyarranged to pass through a portion of the magnetic field with acorrespondingly lesser flux density whereby particles of differentenergies are simultaneously deflected through substantially the sameangle and means for supplying time varying current to the windings ofsaid electromagnet such that the amplitude of the magnetic field betweenthe pole pieces of said electromagnet is controlled as a function oftime thereby to determine the path which the scanning particle beam willtrace.

5. Apparatus for scanning a particle beam containing particles ofdiiferent energies comprising in combination means for bending theparticle beam directed into said Scanning apparatus whereby after thebeam is bent there is a particle energy gradient across the bent beamand means for imparting a scanning movement to the bent beam, saidscanning means including a scanning magnet, the pole pieces of saidscanning magnet having a flux density gradient therebetween whereby thebent beam is directed between the pole faces of said scanning magnetwith the particles of greater energy arranged to pass through a portionof the scanning magnet magnetic field with a correspondingly greaterflux density thereby simultaneously to deflect particles of difi'erentenergies through approximately the same angle.

6. The beam scanning apparatus of claim 5 wherein said bending meansincludes a bending magnet having its pole pieces aligned along oppositesides; of the particle beam and having its output surface tilted at anacute angle to the high energy side of the beam which has emergedtherefrom so that particles of greater energies will travel longertrajectories through said bending magnet and thereby particles of allenergies will emerge from said bending magnet having been bent throughsubstantially the same angle.

7. The beam scanning apparatus of claim 6 including means forpositioning the input surface of said bending magnet with relation tothe particle beam directed into said bending magnet thereby to controlthe spot size and shape of the particle beam issuing from saidapparatus.

8. The beam scanning apparatus of claim 5 wherein said bending means andsaid scanning means are mounted outside an evacuated chamber throughwhich the particle beam passes, said chamber having means for passingthe particle beam into and out of said chamber and having a rotatablecoupling means whereby said chamher, said bending means and saidscanning means can be rotated about the axis of the particle beamdirected into said chamber thereby to direct the scanning beam in anydirection about the axis of the particle beam.

9. Apparatus for bending and scanning a particle beam said apparatuscomprising an evacuated housing with means for passing a particle beaminto and out of said housing, means for bending a particle beam directedinto said housing to thereby form a particle energy gradient across thebent beam, said bending means including a bending magnet mounted withinsaid housing and having means for selecting the angles which the inputand output surfaces of said bending magnet make with the particle beam,and means for imparting a scanning move ment to the bent beam, saidscanning means including a scanning magnet, the pole pieces of whichhave a flux density gradient therebetween said bent beam being adaptedand arranged relative to said scanning means such that said bent beam isdirected between the pole faces of said scanning magnet with the bentbeam arranged so that particles of greater energy pass through a portionof the scanning magnet magnetic field with a correspondingly greaterflux density and particles of lesser energy pass through a portion ofthe scanning magnet magnetic field with a correspondingly lesser fluxdensity whereby particles of different energies are simultaneouslydeflected through approximately the same angle.

16 Apparatus for scanning a particle beam comprising in combinationmeans for bending the particle beam directed into said scanningapparatus and means for oscillating said bending means about an axiscoincident with the axis of the particle beam thereby to bend theparticle beam and impart a scanning movement to the bent beam, saidbending means including a bending magnet with its pole pieces alignedalong opposite sides of the particle beam, said bending magnet havingits output surface tilted at an angle to the emerging beam and havingthe input surfaces of said pole pieces contained in rotatable sectionsof said bending magnet whereby the angle of incidence between theparticle beam and the plane of said input surfaces can be changed byrotation of said rotatable sections thereby adjusting the focusingeffect that the fringe magnetic field of said bending magnet has on theparticle beam passing therethrough.

11. Apparatus for scanning a particle beam comprising in combinationmeans for bending the particle beam directed into said scanningapparatus, means for oscillating said bending means about an axiscoincident with the axis of the particle beam thereby to bend theparticle beam and impart a scanning movement to the bent beam, anevacuated chamber with means for passing a particle beam into and out ofsaid chamber with said bending means and the means for oscillating saidbending means located inside said chamber and rotatable coupling meansrotatably supporting said bending means with said chamber said bendingmeans and said means for oscillating said bending means being adaptedand arranged to direct said scanning beam in any direction about theaxis of the particle beam.

12. Apparatus for scanning a particle beam containing particles ofdifferent energies comprising in combination an evacuated chamberadapted for passing a particle beam therethrough and provided with meansfor rotatable attachment to a particle accelerator; means for bendingthe particle beam path within said chamber whereby after the beam isbent there is a particle energy gradient across the particle beam, saidbending means including a bending magnet fixed around said chamber withits pole pieces aligned along opposite sides of the particle beam path,said bending magnet having its output face tilted at an acute angle tothe high energy side of the beam which has emerged therefrom and havingthe input surfaces of said pole pieces contained in rotatable sectionsof said bending magnet whereby the angle of incidence between theparticle beam and the plane of said input surfaces can be changed byrotating said rotatable sections; and means for imparting a scanningmovement to the particle beam whereby particles of different energiesare scanned through approximately the same angle, said scanning meansincluding a scanning magnet fixed around said chamber with the polefaces of said scanning magnet being of such shape as to create a fluxdensity gradient therebetween whereby the bent beam is directed betweenthe pole faces of said scanning magnet with the high energy side of thebent beam aligned with the high flux density side of the field of saidmagnet thereby to deflect particles of different energies back and forththrough the same angle.

13. A bending magnet for bending a particle beam whereby after the beamis bent there is a particle energy gradient across the bent beam saidbending magnet comprising opposing pole pieces adapted to be aligned onopposite sides of the particle beam, said pole pieces having theiroutput surface tilted at an acute angle to the high energy side of theparticle beam which has emerged from the output surface so thatparticles of greater energies will travel longer trajectories throughsaid bending magnet and thereby particles of all energies will bedeflected through substantially the same angle said acute angle beingless than 60, said acute angle being measured between any given highenergy side particle trajectory emanating from said output surface andsaid output surface, in a direction rotated away from the lower energyside of said bent beam having a particle energy gradient thereacross andthe input surface of said magnet positioned at an angle to the particlebeam directed into said bending magnet thereby to control the spot sizeand shape of the particle beam issuing from said bending magnet.

14. Apparatus for bending and scanning a particle beam said apparatuscomprising an evacuated housing with means for passing a particle beaminto and out of said housing, means for bending a particle beam whendirected into said housing whereby after the beam is bent there is aparticleenergy gradient across the bent beam, and means for imparting ascanning movement to the bent beam, said scanning means including ascanning magnet, the pole pieces of which have a flux density gradienttherebetween whereby the bent beam is directed between the pole piecesof said scanning magnet with the bent beam arranged so that particles ofgreater energy pass through a portion of the scanning magnetic fieldwith a correspondingly greater flux density thereby to deflect particlesof different energies through approximately the same angle.

15'. Apparatus for scanning a particle beam comprising in combinationmeans for bending a particle beam directed into said scanning apparatusand means for oscillating said bending means about an axis coincidentwith the axis of the particle beam thereby to bend the particle beam andimpart a scanning movement to the bent beam, said bending meansincluding a bending magnet with its pole pieces aligned along oppositesides of the particle beam, the output surface of said bending magnetbeing tilted at an acute angle to the high energy side of the particlebeam emerging from said output surface and the input surface of saidbending magnet being positioned at an angle to the particle beamdirected into said bending magnet thereby to control the spot size andshape or" the particle beam issuing from said apparatus.

lid. The apparatus of claim lld wherein said means for bending aparticle beam comprises opposing pole pieces adapted to be aligned onopposite sides of the particle beam, said pole pieces having theiroutput surface tilted at an acute angle to the high energy side of theparticle beam which has emerged from the output surface so thatparticles of greater energies will travel longer trajectories throughsaid bending magnet and thereby particles of all energies will bedeflected through substantially the same angle, and the input surface ofsaid magnet positioned at an angle to the particle beam directed intosaid bending magnet thereby determining the spot size and shape of theirradiating beam of particles issuing from said apparatus.

17. Apparatus for scanning a particle beam with a particle energygradient thereacross including a first means and a second means, saidfirst and second means positioned on oppositesides of said particle beamfrom one another said first and said second means being adapted andarranged to apply deflecting forces having non-zero field densitygradients along the trajectories of the different energy particlesthrough said apparatus such that for all the different particletrajectories through the apparatus all the deflecting forces applied toany given particle is substantially proportionate to the energy of thatparticle thereby simultaneously to deflect particles of differentenergies through approximately the same angle.

18. Apparatus for scanning a particle beam containing particles ofdifferent energies comprising in combination means for bending theparticle beam directed into said scanning apparatus to thereby form aparticle energy gradient across the bent beam and means for imparting ascanning movement to the bent beam, said bending means including meansfor applying particle deflecting forces along the trajectories ofdifferent energy particles through said bending means such that for allthe different particle trajectories through said bending means the sumof all the deflecting forces applied to any given par ticle issubstantially proportionate to the particle energy whereby all theparticles emerging from said bending means have been deflected throughsubstantially the same angle and said scanning means including means forapplying defiecting forces along the trajectories of the differentenergy particles through said scanning apparatus such that for all thedifferent particle trajectories through said scanning means the sum ofall the deflecting forces applied to any given particle is substantiallyproportionate to the particle energy thereby simultaneously to deflectparticles of different energies through approximately the same angle.

19. Apparatus for bending a beam of charged particles having essentiallyequal rest mass energies and a range of kinetic energies whereby afterthe beam is bent there is a particle energy gradient across the bentbeam, said apparatus including means for applying deflecting forces alonthe trajectories of the different energy particles having a range ofkinetic energies forming said beam such that for all the differentparticle trajectories through the apparatus the deflecting forcesapplied to any given particle is substantially proportionate to theenergy of that particle whereby particles of all energies passingthrough said apparatus will be deflected through substantially the sameangle such that there is a particle energy gradient across said bentbeam, means for scanning said bent beam having a particle energygradient thereacross, said scanning means adapted and arranged to applydeflecting forces to said bent beam such that for all the differentparticle trajectories of said bent beam the sum of all the deflectingforces applied to any given particle is substantially proportionate tothe energy of that particle thereby simultaneously deflecting particlesof different energies through approximately the same angle.

20. An apparatus for scanning a particle beam containing particles ofdifferent energy levels randomly dispersed therein comprising firstmeans for transforming said particle beam containing particles ofdifferent energy levels randomly dispersed therein into a particle beamdirected in a different direction with a particle energy gradientthereacross, said first transforming means including means for applyingvariable deflecting forces to the various particles, which forces aresubstantially proportional to the energy of each of the variousparticles, second means positioned downstream of said first transformingmeans for transforming the particle beam with the particle energygradient thereacross into a scanning beam, said second transformingmeans scanning said particle beam such that a ray containing all theparticles of one energy level is scanned through substantially the sameangle as is a ray containing all the particles of a different energylevel, said second transforming means including means for applyingdeflecting forces having non-zero field density gradients, saiddeflecting forces being substantially proportional to the energy of eachof the various particles in said particle beam having a particle energygradient thereacross.

21. Apparatus for scanning a particle beam with a particle energgradient thereacross comprising means for applying to each of thevarious particles in the particle beam with the particle energy gradientthereacross defiecting forces having non-zero field density gradients,which forces are substantially proportional to the energy of each ofsaid various particles in said particle beam with the particle energygradient thereacross, and means for varying said deflecting forces toscan said particle beam such that a ray containing all the particles ofone energy level is scanned through substantially the same angle as aray containing all the particles of a different energy level.

References Cited by the Examiner UNITED STATES PATENTS 2,004,099 6/35Bedford SIS-76 2,551,544 5/51 Nier et al 313-75 X 2,559,657 7/51 Page315-23 2,760,096 8/56 Longini 313- 3,013,154 12/61 Trump 313-84 XFOREIGN PATENTS 1,020,193 11/52 France.

GEORGE N. WESTBY, Primary Examiner.

RALPH G. NILSON, Examiner.

1. A BENDING MAGNET FOR BENDING A PARTICLE BEAM WHEREBY AFTER THE BEAMIS BENT THERE IS A PARTICLE ENERGY GRADIENT ACROSS THE BENT BEAM SAIDBENDING MAGNET COMPRISING OPPOSING POLE PIECES ADAPTED TO BE ALIGNEDALONG OPPOSITE SIDES OF THE PARTICLE BEAM, SAID POLE PIECES HAVING THEIROUTPUT SURFACE TILTED AT AN ACUTE ANGLE TO THE HIGH ENERGY SIDE OF THEPARTICLE BEAM WHICH HAS EMERGED FROM THE OUTPUT SURFACE SO THATPARTICLES OF GREATER ENERGIES WILL TRAVEL LONGER TRAJECTORIES THROUGHSAID BENDING MAGNET AND THEREBY PARTICLES OF ALL ENERGIES WILL BEDEFLECTED THROUGH SUBSTANTIALLY THE SAME ANGLE, SAID ACUTE ANGLE BEINGLESS THAN 60*, SAID ACUTE ANGLE BEING MEASURED, BETWEEN ANY GIVEN HIGHENERGY SIDE PARTICLE TRAJECTORY EMANATING FROM SAID OUTPUT SURFACE ANDSAID OUTPUT SURFACE, IN A DIRECTION ROTATED AWAY FROM THE LOWER ENERGYSIDE OF SAID BENT BEAM HAVING A PARTICLE ENERGY GRADIENT THEREACROSS.